Recently, as renewable energy sources, solar cells that directly convert the light energy of the sun to electric energy (photovoltaic power generation) have been attracting attention. Since the output of solar cells varies depending on the insolation conditions of the sunlight and the like, when the insolation conditions change, there are cases in which it is not possible to efficiently extract electric energy. Therefore, maximum power point tracking (MPPT) control is known in which the optimal operation points are tracking-controlled so that the output of a solar cell is maximized even when the insolation conditions change (for example, Patent Literature 1).